1. Field of the Invention
This invention relates to a method of producing Fe-Ni series alloys having an improved effect of restraining streaks during the etching, and more particularly to a method of producing Fe-Ni series alloys suitable as a material for use in an electronic equipment such as a shadow mask for color television cathode tube, an electron-ray indicator tube or the like.
2. Related Art Statement
Iron-nickel series alloys (hereinafter abbreviated as Fe-Ni alloy) used as a material for a shadow mask of a color television cathode tube are pointed out to have a drawback that white stringer pattern or so-called streak is caused in the production of the shadow mask through photoetching.
As a technique for restraining the occurrence of streak during the etching, there have hitherto been proposed the following methods. For example, Japanese Patent laid open No. 60-128,253 discloses a method of restraining the occurrence of streak, wherein an ingot is heated above 850.degree. C. and forged at a total sectional reduction ratio of not less than 40% per one heat to mitigate a segregation portion of nickel.
Furthermore, Japanese Patent laid open No. 61-223,188 discloses a method of restraining the occurrence of streak, wherein the segregation ratio of nickel and the segregation zone thereof are controlled through the prevention of segregation in the production of ingots or by subjecting to a diffusion treatment of nickel through a heat treatment in the production step of bars.
However, the conventional technique disclosed in Japanese Patent laid open No. 60-128,253 is a method of conducting the forging at the total sectional reduction ratio of more than 40%, but the segregation of various elements can not substantially be restrained since such a forging is under a usually used loading. As a result, it is insufficient to prevent the occurrence of streaks during the etching.
On the other hand, the technique disclosed in Japanese Patent laid open No. 61-223,188 is a method of mitigating the component segregation through the diffusion of Ni based on high-temperature heat treatment. However, since the sheet thickness is thin as compared with the case of heating at the slab stage, the oxidation loss becomes relatively large and the yield considerably and undesirably lowers.
In the above conventional techniques, there is the following problem. That is, in shadow masks for various displays requiring a higher precision as compared with general-purpose television displays, the size of hole to be pierced is smaller by about 1/2 than and also the number of holes is larger by 2 or more than those in the usual case. Therefore, if it is intended to manaufacture such a high precision shadow mask, the quality of the starting material itself depends upon the uniformity of the hole during the etching. However, the conventional techniques can not completely restrain the occurrence of streaks during the etching because the improvement of the material quality is not proceeded at the present.